Speaker enclosure system



y 13, 1965 ZENNOSUKE KUWAYAMA 3,194,340

SPEAKER ENCLOSURE SYSTEM Filed May 15, 1964 v /0 2d 50 m0 2m 40d raw T 1 a a] ZENNOsI/KE K155352321 BY M ATTORNEY United States Patent 3,194,340 SPEAKER ENCLOSURE SYSTEM Zennosuke Kuwayama, 3 Z-chome, Kanda-Awaji-cho, Chiyoda-lru, Tokyo, Japan Filed May 15, 1964, Ser. No. 367,773 3 Claims. (Cl. 181-31) The present invention relates generally to improvements in sound reproducing systems and it relates particularly to an improved enclosure system assoicated with a loud speaker whereby sound reproduction of high fidelity is achieved. This application is a continuation-in-part of copending patent application Serial No. 166,637, filed January 16, 1962 now abandoned.

The conventional high fidelity sound reproducing systems geenrally include enclosure arrangements which possess numerous drawbacks and disadvantages. They are usually of great bulk and highly space consuming and hence inconvenient to use and often unattractive in appearance and generally expensive. Typical of these en closure arrangements are those of the baflle type, closed type, the various horn types, and the bass reflux type. However, when the enclosure device, irrespective of the type, is reduced in volume below its reasonable optimum size there is a consequent rapid drop in the bass response of the sound reproducing system and a marked reduction in the overall fidelity thereof. As is well known, in the typical cone type speaker the sound is emitted from the front and rear of the speaker in opposite directions the sound being of substantially the same wave shape but of opposite phase. Thus, where no compensating arrangement is provided, particularly at the low audio frequencies, these oppositely derived sound waves interfere with and substantially cancel each other in the close vicinity of the loud speaker so that for practical purposes they are highly attenuated in very short distances. The various enclosure arrangements whether of the baffle, horn, reflex bafiie or other type operate either to fully attenuate or absorb the rearwardly directed sound or provide it with a path so that when it reaches the front of the speaker it is substantially in phase with the forwardly directed sound. In either case a certain minimum of space is required for satisfactory results.

It is clear that the size of the baffle necessary to provide a path sufficient to effect a phase reversal is inordinately large. However, in a bass reflex type enclosure the air column formed by the enclosure is caused to resonate, by the action of the sound wave issuing from the rear side of the speaker, and thus the phase of the original sound wave is reversed. This reversed phase wave is emitted from a port in the enclosure separately from the speaker mounting opening, whereby the relative phase of the sounds, particularly of the long wave length bass tone sound, issuing from the front side of the speaker, reinforce rather than cancel each other and high-fidelity sound reproduction is achieved. In the horn type speaker system, a sound passage is provided in the enclosure and with a heavy load the bass tone sound is emphasized. All of these devices, however, are intended for improvements of tone quality making use of the proper nature of an air column with respect to the sound issuing from the speakers rear side. Therefore, diminishing of the enclosure size is limited, and within this limited range still a considerable size is required, and disadvantages accompanying this limitation are the various interferences withthe sound and distortions of reproduced sound which occur.

If the size of the closed enclosure is less than the size suitable to the speaker associated therewith, the air pressure within the enclosure varies excessively as the speaker cone vibrates, and this prevents the cones movement, rendering the faithful reproduction of bass tone sound im- 'ice possible. Therefore, a construction which keeps the air pressure within the enclosure constant even when the size of the enclosure is diminished, would result in superior bass tone sound reproduction.

In the convxentional enclosure, rigid and thick walls have been commonly utilized. This is because if thin plates are used they will vibrate or resonate, resulting in booming or resonance within the enclosure and accordingly lowering the reproduction fidelity and imparting a sound quality which is highly uncomfortable and un-' pleasant for the listener.

If means were provided enabling the closure wall to absorb the vibration energy which is the cause of reproduction fidelity lowering, in a highly effective manner, then such means would be very suitable for absorbing the sound issuing from the rear side of the speaker and further would be of service in preventing booming or resonance when thinner plates are utilized for the enclosure.

As for plate members used for high-fidelity sound reproduction, even when such members are of small area, if such measure should be adopted as to lower the char acteristic frequency of these members so as to be adapted to the bass tone frequency vibration of the speaker cone, the amplified reproduction of bass tone range sound would be possible, as is the case with the air column resonance of bass reflex type enclosure.

It is thus a first object of the present invention to provide an improved enclosure of greatly reduced size in a high fidelity sound reproducing system and to accordingly eliminate the disadvantages that have been present in the conventional installations.

A second object of the present invention is to provide an improved enclosure of the above nature further characterized by, the tone quality of the reproduced sound.

A third object of the present invention is to provide an enclosure of the above type which effects the improved reproduction particularly of bass tone sound so that highfidelity sound reproduction is achieved.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a front perspective view of a speaker unit embodying the present invention;

FIGURE 2 is a transverse sectional view thereof; and

FIGURE 3 is a graph of the frequency response curves of a conventional speaker unit and of such speaker unit modified in accordance with the present invention.

In a sense the present invention contemplates the provision of a speaker unit comprising an enclosure member having a predetermined resonant frequency and including a plurality of opposite walls and a front wall having an aperture formed therein, an electrically energized speaker element mounted in registry with said aperture, and weight members mounted on opposite of said walls, said weight supporting walls having resonant frequencies lower than said predetermined resonant frequency. It should be noted that the predetermined resonant frequency referred to is the resonant frequency in the absence of the weight members.

In the high fidelity reproduction of disc and other types of recordings a limiting factor is usually the resonant frequency of the loudspeaker system or unit. In the area of the resonant frequency there is a sharp increase in sound intensity with a decrease in frequency followed by an externally sharp drop in the sound intensity. Thus the lower limit of the speaker unit frequency response is approximately or somewhat higher than the resonant frequency of the system. It has been discovered that by modifying the speaker enclosure system by the addition of the Weights,

( as set forth above, the sharp rise and drop of the speaker unit frequency response at the resonant frequency of the enclosure is flattened and substantially eliminated to thereby greatly lower the practical low frequency limit of the speaker unit response. This is accomplished at a minimum of expense and it is applicable to great advantage to low cost enclosure units although a highly significant improvement is experienced with larger and more costly enclosures. In addition, with the present structure, the walls of the enclosure may be made of relatively thin panels thereby permitting the economic use of the synthetic organic polymers such as rigid polyvinyl chloride, thin plywood, resin bonded fiber board and the like.

In accordance with a preferred form of the improved speaker unit, the enclosure member comprises a box including parallel rectangular front and rear, top and bottom and side walls, the front wall having a centrally located aperture formed therein and the speaker element is mounted on the front wall in registry with the aperture. The walls are advantageously formed of a thin rigid synthetic organic polymer and means are provided for reinforcing and firmly anchoring the edges of each of the walls. The weights are centrally mounted on each of the walls and are of a value which reduces the resonant frequency thereof to at least fifty cycles per second below that of the enclosure in the absense of the weights. The weight of the speaker element exceeds that of the weight mounted on the rear wall.

Referring now to the drawings and particularly FIG- URES 1 and 2 thereof which illustrate a preferred embodiment of the present invention, the reference numeral generally designates the improved speaker unit which includes an enclosure member 11 and a speaker element 12. The speaker element 12, is of the conventional permanent magnet type, comprising a front frame section 13 provided with rearwardly radially inwardly directed spokes or ribs 14 supporting a magnet mounting bracket 16. A voice coil carrying conical diaphragm 17 projects rear- Wardly from the frame section 13, to which it is peripherally secured, to the magnetic field of the bracket supported magnet.

The enclosure member 11 is a rectangular box including front and rear walls 18 and 19 respectively, top and bottom walls 20 and 21 respectively, and opposite side walls 22. The box walls are thin rectangular panels formed of a rigid resilient material such as a rigid synthetic organic polymer, for example rigid polyvinyl chloride, polystyrene and the like, thin plywood, fiber board for example resin bonded fiber board, etc. The front Wall 13 has a centrally located central speaker opening 23 formed therein and a flat rigid reinforcing frame 25 preferably of the same material as the front wall 18, is rigidly secured to rear border of the aperture 23. The speaker frame 13 is suitably secured to the rear face of the reinforcing frame 25 along the peripheral border of the opening 23.

Suitably aflixed to the inner faces of the top and bottom walls 20 and 21 and side walls 22, such as by cement or the like, and spaced a short distance inwardly from the rear edges thereof, are top and bottom parallel horizontal square bars 24 and side parallel vertical square bars 26, the rear faces of the bars 24 and 26 lying in a common vertical plane. The rear wall 19 telescopes the rear borders of the top, bottom and side walls 20, 21 and 22 and is provided with a suitably secured forwardly projecting peripheral lip 27 having a flat front face abutting the rear faces of the bars 24 and 26 and a flat outer face abutting the confronting faces of the top, bottom and side walls. The rear wall 19 is separably secured to the closure assembly 11 by a plurality of screws 28 passing through openings in the rear wall 19 and lip 27 and engaged aligned tapped bores formed in the bars 24 and 26. Suitably affixed to inner faces of the upper and lower borders of the side wall 19 and the opposite side borders of the top and bottom walls 20 and 21 are forwardly and rearwardly extending, horizontal parallel edge reinforcing bars 29 which contribute to a rigid assembly of the enclosure 11 and terminate in vertical fiat faces in the plane of the front edge of the top, bottom and side walls 29, 21 and 22. The front wall 18 is firmly secured along its rear borders, such as by cement or the like, to the front faces of the bars 29 and the front edges of the top, bottom and side walls. The various walls of the enclosure assembly ll. are advantageously formed of the same material and the other components may likewise be so formed. Foot pieces 3% depend from and are secured to the underface of the bottom wall 21 at the corners thereof.

A mounting block 32 advantageously formed of the same material as the enclosure walls, is rigidly affixed to the inner face of each of the enclosure rear, top and bottom and side walls, 19, 2t), 21 and 22 in any suitable manner. A central mounting bolt 33 is rigidly carried by each of the blocxs 32 and projects inwardly thereof perpendicular to the corresponding supporting wall and is centrally located on and equidistant from the opposite edges of the respective supporting wall. A cylindrically shaped heavy weight member has an axial bore formed therein and engages each of the bolts 33 being locked thereon and firmly pressed into rigid engagement With the outer face of the corresponding mounting block 32 by means of a nut 36 engaging the bolt 33 and tightened against the weight member 34. The weight member 34 may be formed of iron, lead or other heavy material.

The confronting opposite walls of each pair thereof of the enclosure member 11 are of the same configuration and formed of the same material, and the weight members 34 mounted thereon are of about the same value so that said opposite walls possess approximately the same sound characteristics. Each of the weight carrying walls have a resonant frequency less than that of the enclosure member 11 in the absence of the weight members 34 and advantageously at least 50 cycles per second less. The resonant frequency of each of the weight carrying walls is advantageously equal to about the same frequency. The weight of the speaker element is advantageously at least as great as the weight member 34 mounted on the rear wall 19.

The following is an example of a speaker unit constructed in accordance with the present invention, which example is merely employed to demonstrate the superiority thereof over a corresponding conventional speaker unit, it being understood that the subject structure is applicable to great advantage to other enclosures of both greater and smaller size and of different shapes. The dimensions of the rectangular box enclosure member 11 were 250 millimeters wide, 280 millimeters high and 225 millimeters deep and the walls were formed of a rigid or hard transparent polyvinyl chloride of a thickness of 4 millimeters. The speaker aperture 23 and the registering aperture of the reinforcing frame 25 were circular and had diameters of millimeters, the frame 25 being approximately square with a width of millimeters and having its corners removed to provide 43 millimeter edges and being formed of a rigid transparent polyvinyl chloride. Each of the mounting blocks 32 was a 40 millimeter square of 10 millimeter thick rigid polyvinyl chloride secured to the corresponding wall by an epoxy resin cement. The weight members 34 were 50 millimeter diameter, 24 millimeter iron cylinders having weights of about 350 grams, the efiective weight being somewhat increased by the weight of the nut and bolt 36 and 33 and the mounting block 32. The speaker element 12 had a diameter of millimeters and weighed 750 grams.

Referring to the graph illustrated in FIGURE 3, a curve A represents the frequency response in the lower audio range of the speaker unit it specifically described and dimensioned as above and curve B represents the frequency response of the same speaker unit with the weight members 34, however, removed. An inspection of curve B clearly demonstrates that the frequency response of the speaker unit 10 without the weights 34, corresponding to a conventional enclosure, is extremely poor below around 250 cycles per second. At about 250 cycles per second the intensity rises sharply over 6 db to a peak at about 200 area-sac cycles per second and then drops very sharply about 10 db to a trough at about 170 cycles per second and then rises about 4- db to a short plateau at about 150 cycles per second. Thus below about 250 cycles per second, the frequency response of the unweighted speaker unit Would not be considered suitable for high fidelity reproduction since the distortion introduced in the 150 to 250 cycle per second band is excessive.

in contrast to the unweighted speaker unit, the speaker unit Fill described above, as clearly demonstrated by curve A, in the low frequency range peaks at a short plateau at about 130 cycles per second and this plateau is gradually approached from the low frequency side and still more gradually from the high frequency side Which is relatively fiat. Between 110 and 500 cycles per second the specifically dimensioned speaker unit It has a frequency response variation not exceeding about :2 /2 db. Thus with the present expedient the frequency response of the speakor unit has been extended at the low frequency end for at least 73 cycles per second and effectively for much more than that. It is again important to note that radically superior results are achieved by means of the present expedient when applied to speaker enclosures of various sizes, the response curve at the low frequency end being improved and the limit extended even With large enclosures having a normal resonant frequency considerably less than 200 cycles per second.

While there has been described and illustrated a preferred embodiment of the present invention it is apparent that numerous alterations, omissions and additions may be made Without departing from the spirit thereof.

What is claimed is:

1. A speaker unit comprising an enclosure member of substantially rectangular prismatic configuration and having a predetermined resonant frequency and delineated by opposite resonant front and rear, top and bottom and side rectangular Walls, said front Wall having an aperture formed therein, an electrically energized speaker element mounted on said front wall in registry with said aperture, and Weight members substantially centrally mounted on said top, bottom, side and rear Walls, said weight supporting Walls having resonant frequencies at least fifty cycles per second less than said predetermined resonant frequency.

2. A s eaker unit comprising an enclosure member of substantially rectangular prismatic configuration and having a predetermined resonant frequency and delineated by opposite resonant front and rear, top and bottom and side rec tgular walls, said front Wall having a centrally located aperture formed therein, an electrically energized speaker element mounted on said front Wall in registry With said aperture, weight members substantially centrally mounted on said top, bottom, side and rear Walls, said speaker unit being at least as heavy as said weight member on said rear Wall, said Weight supporting Walls having resonant frequencies at least fifty cycles per second less than said predetermined resonant frequency' 3. The speaker unit of claim 2 including means reinforcing the edges of said enclosure Walls.

References fitted by the Examiner UNITED STATES PATENTS 2,7l3,396 7/55 Tavares 181-31 3,101,810 8/63 Doschek l8131 LEO SMILOW, Primary Examiner. 

1. A SPEAKER UNIT COMPRISING AN ENCLOSURE MEMBER OF SUBSTANTIALLY RECTANGULAR PRISMATIC CONFIGURATION AND HAVING A PREDETERMINED RESONANT FREQUENCY AND DELINEATED BY OPPOSITE RESONANT FRONT AND REAR, TOP AND BOTTOM AND SIDE RECTANGULAR WALLS, SAID FRONT WALL HAVING AN APETURE FORMED THEREIN, AN ELECTRICALLY ENERGIZED SPEAKER ELEMENT MOUNTED ON SAID FRONT WALL IN REGISTRY WITH SAID APERTURE, AND WEIGHT MEMBERS SUBSTANTIALLY CENTRALLY MOUNTED ON SAID TOP, BOTTOM, SIDE AND REAR WALLS, SAID WEIGHT SUPPORTING WALLS HAVING RESONANT FREQUENCIES AT LEAST FIFTY CYCLES PER SECOND LESS THAN SAID PREDETERMINED RESONANT FREQUENCY. 